Delay line



Jan. 3, 1956 C. H. HOEPPNER DELAY LINE Filed Sept. 19, 1945 CbNRAD H. HOEPPNER n .5@t$1atent() 2,729,795 DELAY LINE Conrad H. Hoeppner, Washington, D. C. Application September 19, 1945, Serial No. 617,420 g 2 Claims. Cl- 333-29) (Granted under Title 35, .U. Code (1 952), sec. 266) This invention relates to lumped constant artificial transmission lines, suitable for producing a delay of a pulse type waveform.

It is well known in the art that low pass, lumped constant, electrical filter networks possess many electrical characteristics in common with those of long transmission lines. One of these characteristics is the ability to produce time delay of a signal. When a filter is used for this purpose it is generally desirable that delay alone be introduced and that any attendant sig'nal' distortion be low. It is known that an M-derived filter section having an M equal to 1.27 provides the least distortion in that that. value of M will produce practically a uniform time delay of all frequency components up to half the cut-off frequency. To obtain a value of M of 1.27 it is necessary, as can be shown by known. formulas, to adjust the mutual coupling between adjacent inductance coils in the filter so that an inter-coil coupling coefficient of 0.12 to 0.20 is obtained.

An object of the present invention is to construct a small compact artificial transmission line.

Another object of this invention is to construct an artificial transmission line in which all the reactive elements are mounted on a singular supporting member.

Another object of the present invention is to provide an artificial transmission line utilizing lumped reactive components and employing shielding to reduce coupling between adjacent inductances, such shielding being an integral part of the delay line.

Other objects and features of the present invention will become apparent upon a careful consideration of the accompanying drawing and detailed description.

Fig. 1 is an elevational view of a typical artificial transmission line constructed according to the principles of this invention.

Fig. 2 is a cross-sectional view of the preferred type of capacitor employed in the construction of the transmission line of Fig. 1.

Fig. 3 is a schematic diagram showing the equivalent electrical circuit of the transmission line of Fig. l.

Specifically the artificial line shown in Fig. 1 is constructed according to the teachings of the invention and comprises a plurality of inductance coils 10, 11, 12, 13, and 14, alternately positioned with a plurality of capacitors 15, 16, 17, and 18, on a single coaxial supporting shaft 33. The actual physical construction of the inductance coils is not critical but the universal wound type is found to possess certain advantages in this application. The capacitors on the other hand are preferably of the type generally referred to as Button capacitors. As shown in Fig. 2, a typical Button capacitor is a laminated structure comprising alternate circular discs of dielectric material 20, 25, and conducting plates 21, 22, and 26, all of which are provided with a centrally disposed hole. The two end capacitor plates 21 and 22 are provided with such an inner diameter as to cause good electrical contact with an inner conducting clamping sleeve 23, and such an outer diameter as not to 2,729,795 lntented 3' contact an outer conducting clamping sleeve 24. The central capacitor plate 26 is provided with such an outer diameter as to cause a good electrical contact with the outer sleeve 24, and with such an inner diameter as not to contact the inner sleeve 23. The inner and outer sleeves 23 and 24 thus constitute the terminals for the capacitor. Consequently by making the coaxial supporting shaft 33 from a suitable conducting material and by electrically securing the capacitors 15 through 18 thereto at their inner sleeves a common grounded terminal for the filter is obtained. Y

Due to the shielding elfects of the grounded capacitor plates 21and 22 and the alternate positioning of capacitors and inductance coils onthe coaxial supporting shaft 33 the spacing between adjacent inductance coils can be maintained at a minimum and therefore the degree of compactness at a maximum without impairing the desired inter-coil coupling coefficient. Also in order to maintain the spacing between adjacent inductance coils at a minimum the coaxial supporting shaft 33 may be made from a non-magnetic as well as a conducting material. Alternatively the coaxial shaft may be made from insulating material with the inner-sleeve terminals 23 of the capacitors connected together by a separate lead wire.

Too close a spacing between inductance coils and capacitors will produce eddy currents in the grounded plates 21 and 22 0f the capacitors. These eddy currents Will in turn create loading of-the inductance coils and thereby increase the attern lation constant of the line. To avoid the occurrence of sucliaction separate sleevelike spacing elements indicated 28, 29, 30, 31, and 32, and made from a suitable insulating material are provided. In addition to their function as spacers, the sleeves 28 through 32 also serve as forms on which the inductance coils may be wound.

In Fig. 1 all inductances are shown as of essentially the same size. It should be noted that the end inductances 10 and 14 are actually approximately half the size of the other inductances.

An electrical equivalent of the artificial transmission line of Fig. l is shown in Fig. 3 with corresponding elements indicated by similar reference numerals. This line is equivalent to a low pass filter and therefore, for the proper transmission of short pulses, it is desirable, as previously mentioned, that the cutoff frequency be as high as possible. As in a conventional filter, this cutoff frequency is determined by the magnitude of the inductance and capacitance elements constituting the line.

In the construction of a typical line for producing pulse delay the desired cut-off frequency and the delay perieod are specified by design requirements. By means of known formulas, the magnitude of the inductance and capacitance elements may then be calculated. A convenient capacitor diameter (which is usually equal or greater than the inductance coil diameter for positive shielding action) is then selected depending upon the space requirements. An arbitrary allowance of approximately of an inch is then allowed between adjacent edges of each inductance coil and each capacitor to provide insulation and prevent excessive loss of energy from each inductance due to the creation of eddy currents in the grounded plates of the capacitor. With this much established, the ratio of diameter to length of the inductance coils is then established either by the use of standard formulas such as those involving Nagokas constant or by a process of trial and error. Generally speaking, the calculation of this ratio is so complex that the trial and error method with adjustment to a uniform delay of all frequency components is the most feasible. Thereafter the output waveform may be observed on an oscilloscope to determine the amount of distortion due to energy loss in the grounded plates of the capacitors.

If the distortion of waveform is not too great the A inch spacing may be reduced, however it is not practical to go much below this figure because of insulating difficulties,

A typical delay line for producing a delay of 4 micro seconds, havingv a cut-off frequency of approximately 1 megacycle and a characteristic impedance of approximately 500 ohms employs seven capacitances of 2000 micro micro' farads each, six inductances of approximately 400 micro henrieseach and two end inductances of approximately 200 micro henries. The capacitors were chosen inch in diameter and the coils /2 inch and inch respectively Wound upon spacer sleeves of inch diameter. Spacing of inductances center to center was approximately /8 inch.

The invention described herein may be manufactured and used by or for the Government ofthe United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. An artificial transmission line comprising a rod like conducting member, a plurality of insulating sleeve members each of which contains an inductance coil wound thereon, said sleeve members being disposed on said rod-like member and supported in colinear relation thereby, the separate inductance coils being connected in series, a plurality of disc shaped capacitors each of which includes a centrally disposed conducting sleeve extending therethrough and defining one electrode terminal of the capacitor, the other electrode terminal of the capacitor being formed on the periphery of the capacitor, each of said capacitors being disposed on said rod in alternation with said insulating sleeves with the central electrode of each of said capacitors contacting said rod, the other terminal of each of said capacitors being connected to the electrical junction of adjacent inductance coils.

2. An artificial transmission line comprising a rodlike conducting member of non-magnetic material, a plurality of insulating sleeve members each of which contains an inductance coil wound thereon, said sleeve members being disposed on said rod-like member and supported in colinear relation thereby, the separate inductance coils being connected in series, a plurality of disc shaped capacitors each of which includes disc shaped capacitor plates having a centrally disposed conducting sleeve extending therethrough defining one electrode terminal of the capacitor, the other terminal of the capacitor being formed on the periphery thereof, each of said capacitors being disposed on said rod in alternation with said insulating sleeves and with the central electrode of each of said capacitors contacting said rod, the other terminal of each of said capacitors being connected to the electrical junction of adjacent inductance coils, the diameter of said capacitor plates being at least equal to the diameter of said inductance coils so as to form a partial shield between adjacent inductance coils.

References Cited in the file of this patent UNITED STATES PATENTS 2,163,775 Conklin June 27, 1939 2,181,982 Tarzian Dec. 5, 1939 2,416,297 Finch Feb. 25, 1947 FOREIGN PATENTS 662,395 Germany July 12, 1938 

